Use HeaderBar without TitleBar

Support & Help Requests
1

Some apps are supposed to be without titlebars. E.g. Peek, Gnome-calculator.
But they aren't in my Mate desktop environment (Ubuntu 18.04)

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How to remove titlebars here?
I guess it's possible to run applications with some environmental variables to do so.

2

Ok now i confused.
I found second gnome-calculator with same version on my system. It's located in /snap/bin/gnome-calculator
I've made a screenshot both of them.
So why does it not have title-bar (as I want for all apps) and why does it have different appearance from my default theme?

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